Thermal responsive device



Feb. 28, 1933. COHN ET AL 1,899,558

THERMAL RESPONSIVE DEVICE Filed Sept. 8, 1930 Ihvehtors:

AIFYed COhh, Franz Dausihger, b5 Mm Their Atborheg.

Patented Feb. 1933 UNITED STATES PATENT OFFICE ALFRED COHN, 0F IBEBLIN-CHARLOTTENBURG, AND FRANZ DAUSINGEB, OF BERLIN- TBEPTOW, GERMANY, ASSIGNOBS TO GENERAL ELECTRIC COMPANY, A CORPORA- TION OF NEW YORK THERMAL RI'SPONSIVE DEVICE Application filed September 8, 1930, Serial No. 480,418, and in Germany December 8, 1929.

The invention relates to snap action thermal responsive devices, and provides an improved electrically heated device which under the influence of the ohmic loss produces a snap action by means of a resilient member, such as a leaf spring, for the purpose of actuating a switch contact or releasing the latch mechanism of an overload switch.

In accordance with the invention the two end bearing points for the resilient leaf spring are relatively movable towards and away from each other and are influenced in their position by means of a bimetallic member, for example, a bimetallic strip. Thus under the influence of the ohmic loss, this bimetallic member carries out a movement which is transmitted to the relatively movable end bearings for the leaf spring so that their distance apart increases with the increasing temperature. When the end bearings are separated a predetermined distance which corresponds to a predetermined temperature of the bimetallic member, the leaf spring suddenly executes a snap movement.

A particularly simple construction is obtained if, for example, a slit bimetallic strip without further intermediate members is made into the carrier of one of the bearings and the current made to pass directly through the bimetallic strip. Both bearing carriers can, of course, also be formed as bimetallic strips.

Various constructional examples of the invention are represented in the drawing in which Fig. 1 is a perspective view of the improved device; Figs. 2 and 3 schematically represent various operating positions of the device shown in Fig. l Figs. 4 and 5 illustrate a modification of the invention; Fig. 6 schematically shows an additional modified form and Fig. 7 shows a still further modified form of our invention.

In the device shown in Fig. 1 two slotted bimetallic strips 6 and c are secured at the slotted end in spaced apart relation on a baseplate a. Each of these bimetallic strips at its unslotted or free end has an insulating piece d which is provided with a bearing slot. Between the two slots in the insulating pieces the leaf spring e is extended so that it may be pressed from its normal upward convex over-center position which it has in its free condition and thus assume a downward convex over-center position as shown.

As indicated in Fig. 2 the two bimetallic strips may be so arranged that upon heating they are bent outwards in the direction of the arrows. In this way the bearing pres- I sure on the ends of spring 6 is diminished and it suddenly snaps over into its normal upward convex position as indicated in Fig. 3. By this reverse snap action movement the spring may, for example, open a contact or strike on the pawl device of an overload switch in order to release the latter. The invention is particularly suited in this form for time element thermal switches, motor protective switches and similar thermal overload indicating and controlling arrangements. Thus, for example, the bimetallic strip 6 may be located in one phase of the motor supply line and the bimetallic strip a, if desired, in another phase.

Also means can be arranged for varying the releasing limiting current strength, for example, by varying the distance apart of the bearing points by suitable means. The same result may be obtained by shunt resistances so which are connected in parallel to the bimetallic strip and preferably so near thereto that their heat can also be used for heating the "strip. Moreover the strips, in place of being traversed direct by current, can, of course, also be heated indirectly by heating windings, transformers, or in any other suitable way. Furthermore, the flexed position of the leaf spring ready for operation can, for example, be reestablished by hand, as by means of a knob J which can be depressed to engage the leaf spring, or by means of an electromagnet, or in the case of switches, by the disconnecting and connecting movement.

If the thermal responsive device is so made that the bimetallic strips are not bent in opposite directions but both in the same direction as indicated in Figs. 4 and 5, then the leaf spring will not snap over as long as the two similar bimetallic members have equal temperature- If, however, the temperature of the stri is greater than that of strip 7), then the lea spring under these conditions snaps over. With this construction the device can be used, for example, as a differential relay for the control of current differences in two supply lines.

A further possibility of use is afl'orded for multiphase plants by the modified arrangement shown in Fig. 6. Between the three bimetallic strips 6, c, and f are arranged "leaf springs g and h. The snap movement may be traversed by the current or heated indirectly. By this means, different effects can be obtained, for example, the snapping over temperature of the leaf spring canbe reduced when it is arranged so that through its own bending its tension is reduced as a result of the heat. On the other hand, the temperature for the snap-over movement can be increased by means of a corresponding arrangement.

The device allows of further advantageous use if, according to the invention, one of the two bearings is secured on a bimetallic strip 0 (Fig. 7 )or allowed to be controlled by such a onewhich is not heated by the current, but which is only subjected to the influence of the surrounding temperature and which, in the case of increase of temperature, moves its bearing in the same sense as does the current-heated strip 5 with the second bearing. By this modified arrangement, a compensation of the room temperature is obtained. The releasing limit current intensity then remains, independently of the room temperature, always the same because the distance apart of the bearing points in the case of each room temperature remains the same so long as no current flows. By means of such compensated arrangements, for example, very accurately acting over-load releases can be provided. The arrangement has the further advantage that the releasing limit temperature need no longer be selected relatively high with regard to the influence of the room temperature, as is necessary without compensation, but can be kept almost as low as desired, that is, with the releasing current intensity, it can be lowered very much more than without compensation. Thereby, also the watt consumption of such elements can be reduced almost as desired and, on the other hand, the heat time constant be increased as desired because relatively thick cross-sections traversed by current can be used.

A further means of reducing the releasing limiting current strength, according to the invention. consists in mechanical arrangements which relieve the preliminary tension of the leaf spring to such an extent that it is pressed almost as far as the dead center. This can be obtained, for example, by raising the middle of the leaf spring 0, as shown in 'Fig. 7,'by means of a stop screw 71.

What we claim as new and desire to secure by Letters Patent of the United States 1s:

1. A thermal responsive device comprising a pair of bimetallic supports, a resilient member mounted between said supports and arranged under the control of said supports for snap action flexure from one over-center position to an opposite over-center position, and means independent of said supports for returning said resilient member to said one over-center position.

2. In a snap action thermal responsive device, a pair of bimetallic spaced apart supports, a resilient member arranged between said supports and biased for snap action flexure from one over-center position to the opposite over-center position upon the predetermined separation of said supports, said resilient member being normally held by said supports in said one over-center position against its bias to said opposite over-center position, and means independent of said thermal responsive'means for returning said resilient member to said one over-center position.

3. In a snap action thermal responsive device, a pair of bimetallic supports, a resilient member normally held by said supports in one over-center position against its bias to the opposite over-center position so as to snap from one of said positions to the other of said positions under the control of said supports, means independent of said bimetallic supports for returning said resilient member to said one over-center position, and means for subjecting each of said supports to a different temperature condition 4. A multiphase thermal responsive device comprising, a bimetallic support for each phase, resilient members normally held between said supports in one over-center position against its bias to the opposite overcenter position, means for heating each of said bimetallic supports in accordance with an electrical characteristic of a corresponding one of said phases, the said supports controlling the release of said resilient members in response to diiferences in electrical characteristics between said phases, and means independent of said supports for returning said resilient members to said one over-center position.

5. A thermal responsive device comprising a pair of bimetallic supports each of which is slotted to provide a current path therethrough for heating said supports and a resilient member mounted between said supports and biased to one over-center position, said supports normally maintaining said member against its biasin an opposite overcenter position until released by a predetermined heating of said supports, and means for returning said member to said one overcenter position.

6. A thermal responsive device comprising a pair of bimetallic supports each of which is slotted to form a heating current path therethrough, a resilient member mounted between said supports and biased for snap action, said supports being arranged to move in the same direction in response to the heating thereof so as to release said resilient member only in response to a difference in the heating of said supports.

7. A thermal responsive device, comprising a resilient member, a pair of bimetallic supports therefor arranged to be moved in the same direction in accordance with changes in temperature and slotted to form independent current paths in each of said supports, the said resilient member normally being flexed between said supports and operated in response to differences in current flow between said current paths.

8. A thermal responsive device diflerentially responsive to current flow in a plurality of circuits, comprising a slotted bimetallic support for each circuit, resilient members normally biased in one direction between said supports, the said supports in response to an unequal current flow in said circuits releasing said resilient members for movement in accordance with said biases.

In Witness whereof, we have hereunto set our hands this 9th day of August, 1930.

ALFRED COHN. FRANZ DAUSIN GER. 

